Radio telephone system and method of registering an ID code therein

ABSTRACT

A radio telephone system which comprises a base unit (1) connected to a wire line (3) and at least one radio telephone set (2) to be coupled with the base unit (1) through a radio circuit, and in which coupling between the base unit and the radio telephone set is controlled on the basis of an identification code. A non-volatile first memory (58) having an identification previously written therein is provided in one of the base unit (1) and the radio telephone set (2), and an optionally writable second memory (60) is provided in the other. Written in the second memory (60) is a predetermined identification code on the basis of the identification code stored in the first memory (58).

This is a continuation of application Ser. No. 07/340,091, filed Jan.13, 1989 now U.S. Pat. No. 5,097,500.

TECHNICAL FIELD

The present invention relates to radio telephone systems and, moreparticularly, to a radio telephone system which allows the easymodification of identification code (ID code).

BACKGROUND ART

A prior art system of the type referred to is arranged as shown in FIG.11.

A base unit 1, which is coupled through a radio communication circuit toa wireless telephone set 2, is also connected to a wire telephone line3.

The outline of the operation of the base unit 1 will be explained in thefollowing.

A signal transmitted from the wire telephone line 3 is applied through aline relay 33 and a hybrid circuit 4 to a transmitter 5 to be modulatedthereat and to obtain modulated radio waves. The modulated radio wavesare sent through an antenna duplexer 6 to an antenna 7 to be transmittedfrom the antenna to the radio telephone set 2.

Radio waves transmitted from the radio telephone set 2, on the otherhand, are received at the antenna 7 and then sent through the antennaduplexer 6 to a receiver 8 to be demodulated therein and to obtain ademodulated signal. The demodulated signal is sent onto the wiretelephone line 3 through the hybrid circuit 4 and the line relay 33.

A synthesizer 9 outputs a frequency corresponding to a radio channel tothe transmitter 5 and the receiver 8.

One output of the receiver 8 is applied to a received-electric-fielddetecting circuit 10 to determine the intensity of the received electricfield. This circuit 10 is usually called a carrier squelch circuit or anoise squelch circuit.

The other output of the receiver 8 is output as a data signal includedin the received demodulated waves, that is, it is applied to anidentification signal detecting circuit 11 to be compared with anidentification signal that is determined by a combination of the baseunit 1 and the radio telephone set 2. This identification signal isgenerally called an ID code.

An output of the detection circuit 11 and the demodulated output of thedata signal of the receiver 8 are input to a control circuit 12 to beused for control of interconnection. The control circuit 12 in turncontrols the synthesizer 9 for control of the radio channel, and alsocontrols to cause the supply of a transmission data signal to thetransmitter as a modulation input.

Similarly to the base unit 1, the radio telephone set 2 also has anantenna 13, an antenna duplexer 18 and a receiver 14, in which ademodulated output of the receiver 14 is sent to a telephone receiver15. A voice input signal from a telephone transmitter 16 is applied to atransmitter 17 to be modulated and then sent through the antennaduplexer 18 to the antenna 13, from which the voice signal is radiatedin the form of radio waves.

A synthesizer 19, a received-electric-field detecting circuit 20 and anidentification signal detecting circuit 21 are the same as those in thebase unit 1, and a control circuit 22 performs control over the radiotelephone set 2. A loudspeaker 23 is a sounder which emits a callingvoice indicative of a receiving call.

With respect to the power of these circuits, the base unit 1 isconnected through an AC plug 24 to a commercial AC 100 V plug receptacleso that outputs of a rectifier and stabilizer circuit 25 are distributedto the respective circuits of the base unit. One of the outputs of thecircuit 25 is also supplied through a current control resistor 26,charging terminals 27 and 28 to a chargeable battery 29 to use theoutput of the battery 29 as the power of the radio telephone set 2.

The control of the above prior art example in a signal reception modewill be schematically shown in FIG. 12.

More specifically, when the base unit 1 detects a ringing signal fromthe wire telephone line 3 at a ringing-signal detector 30 in an awaitmode (step 34), the unit 1 sets the synthesizer 9 for the controlchannel and turns ON the transmitter 5 to transmit the received signal(step 35). The received signal includes a signal specifying a speechchannel (S-CH).

The radio telephone set 2, on the other hand, turns ON the synthesizer19 for a period of a predetermined time t1 in an await mode to set thesynthesizer for the control channel and also turns ON the transmitter 14(step 36). Under such a condition, if the radio telephone set 2 receivesthe received signal (step 37), then it turns ON the transmitter 17 (step38), transmits an answer signal including the ID code in response to thereceive signal (step 39), and switches the speech channel (S-CH) to thespecified one (step 45). When the radio telephone set 2 receives noreceive signal, it turns OFF the synthesizer 19 and the receiver 14 fora period of a predetermined time t2 (step 40). The intermittent signalreception of the receiver 14 based on its ON and OFF operations iscalled battery saving.

More in detail, assuming that the receiver 14 in its OFF state consumesa current I OFF and the receiver 14 in its ON state consumes a current ION, then an average consumption current IA in the await mode of theradio telephone set 2 is expressed as follows.

    IA=(t1×ION+t2×IOFF)/(t1+t2)

Since a relation of I ON>I OFF is usually satisfied, the averageconsumption current IA can be made small.

The base unit 1, when detecting radio waves transmitted from the radiotelephone set 2 at the received-electric-field detector 10 (step 41),stops the transmission of the received signal (step 42). At this stage,if the field detector 10 detects no radio waves, then the base unit 1continually transmits the received signal up to a predetermined numberof times n (step 43). The predetermined-time transmission is due to theintermittent reception of the radio telephone set 2. That is, the radiotelephone set 2 cannot receive the transmitted signal for a time periodof t2, and thus the transmission is carried out preferably for a periodof a time longer than the time t2 by an amount corresponding to 2received signals. The abortion of the transmission up to n times is dueto the avoidance of the useless occupation of the control channel in theevent where the radio telephone set 2 is powered off or located a longdistance from the base unit 1.

Next, when the ID code included in the received-signal answer signalfrom the radio telephone set 2 coincides with the ID code set for thebase unit 1 (step 44), the base unit 1 switches the speech channel S-CHto the one specified by the received signal. If the two ID codes do notcoincide, then the received answer signal is the one from another radiotelephone set and thus the base unit waits until the ringing from thewire telephone line 3 is terminated (step 47) and returns to its awaitstate.

After switching to the speech channel, the base unit 1 transmits a bellringing signal (step 47). The radio telephone set 2, when receiving thebell ringing signal (step 48), controls the sounder 23 to generate acalling sound (step 49). Under this condition, an off-hook operation ofthe radio telephone set 2 (step 50) causes the telephone set 2 totransmit an off-hook signal (step 51), thus putting the telephone set inits speech mode (step 55).

On the other hand, the base unit 1, when receiving the off-hook signal(step 52), stops the transmission of the bell ringing signal (step 53),and closes the line relay 33 to establish a speech loop with the wiretelephone line 3 and enter its speech mode (step 54).

When the number of transmission times at the transmitter reaches n, thebase unit detects the termination of the signal reception (step 56) andreturns to its await mode, thereby preventing the unnecessarysignal-reception re-operation.

In this way, it is ensured to establish a radio telephone set loop onlywith a party having a coincided ID code, thereby preventing anyerroneous interconnection and telephone charges resulting from radiointerference. The respective ID codes are previously written inassociated ID ROM's 58 and 59, and the ID ROM's are both of anelectrically non-volatile type to avoid the extinguishment of such IDcodes even in case of a power failure.

Such a system as mentioned above has had a problem that since the baseunit 1 and the radio telephone set 2 have respectively ID codes fixedlywritten in the associated ID ROM's, when it is desired to modify thecombination therebetween or add a new combination, it is necessary toopen the respective casings of the unit 1 and telephone set 2 and toexchange the previously written ID ROM's or add new ones. For example,when it is desired to use a plurality of radio telephone sets withrespect to the single base unit 1 or to move a radio telephone set toanother place and to establish a radio circuit between the telephone andanother base unit, it has been impossible for the prior art system torealize it.

In view of such circumstances, it is an object of the present inventionto provide a radio telephone system which eliminates the above problemin the prior art and which allows the easy addition and modification ofcombinations between radio telephone sets and base units.

DISCLOSURE OF INVENTION

In accordance with the present invention, an ID ROM is provided ineither one of a base unit or a radio telephone set and a means forwriting the ID code of the base unit is provided in the radio telephoneset. Alternatively, the means for writing the ID code of the radiotelephone set may be provided in the base unit.

Since the ID code fixedly attached to the base unit or radio telephoneset can be written in the party side according to the present invention,the improvement of the system including the arbitrary combination changeand the addition of the radio telephone sets can be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1, 2, 3, 4, 6, 8 and 9 are block diagrams showing differentembodiments of the present invention, respectively;

FIGS. 5, 7 and 10 are flowcharts for explaining the operations of FIGS.4, 6 and 9, respectively;

FIG. 11 is a block diagram showing a prior art example; and

FIG. 12 is a flowchart for explaining the operation of the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, there is shown a first embodiment of the presentinvention, in which the ID ROM 58 is a non-volatile memory. When theradio telephone set 2 is connected to the base unit 1 to charge thebattery 29, a charging current flows through the charging terminals 27and 28. This causes a voltage at one end of the resistor 26 located onthe side of the terminal 27 to drop from Vcc (for example 8 V) to thevoltage of the battery 29 (for example, 4 V). When a charge detectingcircuit 64 detects such a voltage drop, the base unit detects theinterconnection with the radio telephone set. The control 12 then sendsthe contents or ID code of the ID ROM 58 to the control circuit 22 ofthe telephone set 2 through the route of a signal line a, a switchcircuit 64, ID code write terminals 63 and 63', a switch circuit 62 anda signal line f. The control circuit 22 in turn writes the received IDcode of the ID ROM 58 into an ID-code writing RAM 60 and subsequentlyexecutes such control as earlier mentioned based on the ID code.

After the ID code has been written in the RAM 60, the switch circuits 61and 62 are switched under control of signals on lines c and g asconnected to their positions opposite to those in FIG. 1, so that thewritten ID code is sent through the route of a signal line e, the switchcircuit 62, the ID code write terminals 63' and 63, the switch 61 and asignal line b to the control circuit 12 to be compared with the contentsof the ID ROM 58. As a result, it can be reliably checked whether or notan improper contact between the terminals 63 and 63' or the like haslead to a failure in the correct writing of the ID code, and thus theradio circuit control can thereafter be carried out with a sufficientlyhigh reliability.

When the base unit 1 finds a non-coincidence between the ID codes as aresult of the comparison or receives no ID code, a sounder 65 providedin the base unit 1 may issue an alarm sound or other proper indicationmay be provided.

Shown in FIG. 2 is a second embodiment in which a switch 66 for thewriting of ID code is provided in the base unit 1. The provision enablesthe realization of such ID code write operation as mentioned earilieronly when the switch 66 is turned ON under such a condition that theradio telephone set 2 is connected to the base unit 1.

With such an arrangement, the write operation can be executed only whenit is desired to change the combination between the base unit 1 and theradio telephone set 2 to thereby prevent the unnecessary write operationduring the usual operation, thus avoiding the failure of theinterconnection therebetween due to the improper write operation.

It is not required to provide the ID code write switch 66 always in thebase unit 1, and the switch may be provided in the radio telephone set 2to transmit writing start information to the base unit similarly to theID code.

FIG. 3 shows a third embodiment wherein the radio telephone set 2 isprovided with a non-volatile ID ROM 59 and a dial key pad 32', the padhaving an abbreviated dial key (M) a pause key (P) and an ID code writekey (ID).

The setting of the abbreviated dialing function is carried out throughthe ID code write terminals 63' and 63 or the radio circuit and theabbreviated dial number is stored in a RAM 67 of the base unit 1. TheRAM is backed up by a power supply backup circuit 68 (using a capacitoror a dry cell) to prevent the contents of the RAM from being erased evenwhen the AC power source of the base unit 1 is turned OFF.

In this way, a non-volatile ROM is provided in the radio telephone set 2that is relatively unstable in its power supply to prevent the erasingof the ROM even in case of a power failure, whereas a RAM is provided inthe base unit 1 that is relatively stable in its power supply and thatinvolves a less spatial problem even with the addition of the powerbackup circuit therein, the RAM also being used as an abbreviated dialmemory so as to eliminate the need for rewriting the ID code except foreliminate the need for rewriting the ID code except for modifying thecombination of the ID code and the expansion of the system.

There is shown in FIG. 4 a fourth embodiment of the system which isexcellent in the expansion ability or expansibility of the system, andin which a base unit 1' can be coupled with a plurality of radiotelephone sets. In the embodiment of FIG. 4, two radio telephone sets 2and 2' are provided as an example.

Explanation will now be made as to how to expand the system of usingonly the single radio telephone set 2 by adding the radio telephone set2' to it.

Assume that the ID code written in the ID ROM 58 of the base unit 1 is"012345". When it is desired to write an ID code in the radio telephoneset 2' in the same manner as mentioned earlier, the operator pushes anID code write key ID provided on a dial key pad 69 and then pushes onenumber key thereon. In this case, since the radio telephone set 2'corresponds to the second one in the system, when the operator pushes anumber key denoted by "2", an ID code "0123452" is written in the radiotelephone set 2'.

That is, the radio telephone set 2 has an ID code of "0123451" and thusthe two radio telephone sets 2 and 2' have their ID codes whichrespectively comprise a common ID code part "012345" and different IDcode parts "1" and "2" added thereto providing a distinction between thetwo.

In the illustrated embodiment, even when any of the radio telephone sets2 and 2' gives a call, they are coupled to the base unit in response tothe common ID code part. At the time of receiving a call, either one ofthe two telephone sets can be sounded by previously selecting one of thetwo telephones for the ringing tone to be sounded.

This control is carried out based on the software of microprocessorswhich form the cores of the control circuits 12, 22 and 22', as shown bya flowchart in FIG. 5.

When receiving a call (step 34), the base unit 1' reads out a previouslyselected received-call select number n from the RAM of themicroprocessor (step 75). That is, this number is previously input orstored in the RAM with use of, in the example of FIG. 4, a select key"S" of the dial key pad 69. For example, the pushing of the select key"S" and a number key "1" means n=1, that is, the radio telephone set 2is previously selected. In the case of the pushing of the keys "S" and"0", that is, n=0, the sounder 65 of the base unit 1' is specificallydesigned to sound (step 76) (step 78). With such an arrangement, theincoming call can be arbitrarily received with use of any of the handset72 of the base unit 1' and the radio telephone sets 2 and 2'. In otherwords, under this condition, since the radio function of the base unit1' is not used, a speech may be realized through the radio circuitestablished based on the outgoing-call coupling control of the radiotelephone set 2 or 2' or through the handset 72. When the operator picksup the handset 72, this causes a hook switch 70 to be turned ON so thatthe operator can have a conversation with the party with use of ahandset transmitter 74 and a handset receiver 73 through a hybridcircuit 71.

In the case of n=1 or 2, set the ID code to be "012345n" (step 77). Thetransmission of the ID code attached to the incoming-call signal enablesthe selective calling of the radio telephone set 2 or 2'.

Shown in FIG. 6 is a fifth embodiment, in which case the radio telephoneset 2 is provided with a fixed, non-volatile ID ROM 59. The pushing ofthe ID key causes the ID code to be stored in the RAM 67 through the IDcode write terminals 63' and 63 in the same manner as mentioned earlier.

The RAM 67 can store therein a plurality of ID codes identifiedaccording to the addresses of the RAM. For example, when it is desiredto write the ID code of the radio telephone set 2 at the address 1, thewriting is carried out by pushing keys "S" and "1" of a dial key pad 69'in the base unit 1' and then pushing the ID key of the dial key pad 32in the radio telephone set 2.

Similarly, the ID code of the radio telephone set 2' is also stored, forexample, at the address 2 of the RAM 67.

The system after the storage of these telephone ID codes is operated foran incoming call as shown by a flowchart in FIG. 7. That is, as in thecase of FIG. 4, the address n of a radio telephone set intended toreceive the incoming call is previously registered with use of theselect key "S" so that, at the time of receiving the incoming call, thebase unit reads out the address n (step 75) and then reads out the IDcode at the address n from the RAM 67 (step 79) to perform its operationfor the incoming-call.

Referring to FIG. 8, there is shown a sixth embodiment in which theradio telephone sets 2 and 2' are the same as those of FIG. 6, a radiotelephone set 2" has a fixed, non-volatile ID ROM 59, and a base unit 1"also has an ID ROM 58 and a RAM 67. That is, connection for thereceiving-call is effected with respect to the radio telephone set 2".Call emission can be achieved from any of the radio telephone sets 2, 2'and 2", when the ID codes of the radio telephone sets 2 and 2' arepreviously stored in the RAM 67 similarly to the example of FIG. 6.

In the present embodiment, in the case where an incoming call, which isintended for the user of the radio telephone set 2, is received at theradio telephone set 2", the pushing of a transfer key "T" and a numberkey indicative of the address (for example, 1) of the radio telephoneset 2 by the user of the telephone 2" causes the base unit 1" to oncebreak the radio circuit with the radio telephone set 2" and subsequentlyto perform its incoming-call coupling control with respect to the radiotelephone set 2 with use of the ID code as the contents at the address1, whereby the incoming call can be received at any of the radiotelephone sets. This system is convenient in the case where, forexample, there is stationed a person in charge of answering thetelephones of the system, and the person may watch only the radiotelephone set 2".

The present embodiment can execute its operations for incoming andoutgoing calls with good reliability, because the system of theembodiment can be conveniently expanded and at the same time only onepair of ID codes cannot be erased in any case.

Although the write operation has been executed through the ID code writeterminals 63 and 63' in the foregoing embodiments, the present inventionis not restricted to the illustrated specific write means. As a matterof course, it is also possible to use the radio circuit as shown in FIG.9 (showing a seventh embodiment).

The seventh embodiment is different from the first embodiment in thatthe ID code write terminals 63 and 63' are not provided and controllines h and i are added.

At the initial stage, the system cannot perform its operation foroutgoing and incoming calls because no ID codes are written in the IDRAM 60. After the radio telephone set 2 is connected to the base unit 1and the charging operation detector 64 detects this connected state asalready explained earlier, however, the turning ON of the off-hookswitch 31 causes the base unit 1 to accept only once the transmissionhaving an ID code not equal to the ID code thereof, establish the radiocircuit and write the ID code in the memory. The above operations willbe explained by referring to a flowchart of FIG. 10.

Steps 80 to 92 show usual call-emission control. When the radiotelephone set 2 issues a call (step 80) and confirms an idle speech C-CH(steps 81 and 82), the telephone set 2 checks whether or not the ID codeis already written in the ID RAM 60 (step 93). When the ID code is notwritten, the telephone set 2 acts to reduce the output of thetransmission through the control signal line i and turn ON thetransmitter 17 to transmit the ID code "0" as a transmission signal(step 94).

The base unit 1, when receiving the transmission signal from the radiotelephone set 2 (step 89), detects the presence or absence of the outputof the charging operation detector 64 (step 95). Since the output ispresent, the base unit 1 judges whether the ID code is "0" or not (step96). If the ID code is not "0", then the base unit is put again in theawait condition because of the presence of interference from otherdevices, whereas, if the ID code is "0" then the base unit acts toreduce the output of the transmission through the control signal line hand turn ON the transmitter (step 97) to transmit an answering signal(step 91).

The radio telephone set 2, on the other hand, writes the received IDcode in the ID RAM 60 in response to the answering signal (step 98),switches the speech channel S-CH to the specified one (step 106),transmits the ID code (step 103), stops the transmission (step 104), andreturns to its await mode.

The base unit 1, when confirming that the received ID code coincideswith the contents of the ID ROM 58 (step 100) during the write operationof the ID code (step 99), causes the sounder 65 to generate aconfirmation tone (such as "pee . . . ") (step 101). In the case of anon-coincidence between the ID codes, the base unit causes the sounder65 to issue an alarm tone (such as "pee, pee, pee") (step 102), stopsthe transmission (step 105) and returns to the await mode.

In the case of using the radio circuit, the normal transmission outputusually increases the possibility of having an interferential effect onother devices. However, since the present embodiment is designed toexecute the writing of the ID code only under such a condition that theradio telephone set 2 is connected to the base unit 1, a very low powerand very weak radio waves are sufficient to normally operate the presentembodiment, thus reducing the increase of the interference possibility.

In the present embodiment, further, since the write operation isrestricted to only once, it is preferable to provide a timer or add thecontrol operation. Furthermore, how to control the system, how to usethe radio channel and so on may be arbitrarily modified so long as theydo not depart from the scope of the subject matter of the presentinvention.

For example, the invention may be arranged so that, instead of turningON the off-hook switch with the base unit connected to the radiotelephone set, the turning ON of the off-hook switch and then theconnecting of the radio telephone set to the base unit in apredetermined time (for example, 3 seconds) will enable the realizationof the write operation of the ID code, or so that the execution of suchoperation even without the unit-telephone interconnection will enablethe realization of the write operation of the ID code.

In the case where it is unfavorable that anyone can arbitrarily performthe write operation of the ID code, the invention is arranged so thatthe ID code write operation can be attained, for example, only when theoperator previously inputs a secret number through the dial key pad 69'to previously store it in the RAM 67 and at the time of writing the IDcode, only when he or she inputs the secret number that coincides withthe one previously stored in the RAM 67.

The present invention is not limited to the foregoing embodiments butmay be arbitrarily modified in the scope of the subject matter of theinvention.

For example, in the case where only once write operation is required, itis suffice to use a one-time PROM or it is possible to use anelectrically re-writable, non-volatile ROM called E² PROM, in place ofthe part explained above as the ID RAM. In addition, the ID code aloneis not used, but some signal may also be added to the ID code or it maybe possible to write some signal in a part of the ID code may be writtenaccording to the present invention.

INDUSTRIAL APPLICABILITY

As has been disclosed in the foregoing, in accordance with the presentinvention, the arbitrary modification of the combination between a baseunit and a radio telephone set as well as the additional installation ofanother base unit or radio telephone set can advantageously realizedhighly easily and reliably.

Since the present invention allows the arbitrary modification of theunit-telephone combination, not only the unit and telephone in thecombination can be changed but also a faulty counterpart in thecombination can be readily exchanged for a new one. As a result, thesystem of the present invention is good in maintenance and high inmanufacturing flexibility because of the arbitrary combination.

I claim:
 1. A radio telecommunication system, comprising:a first radiounit having an identification code; a second radio unit; generatingmeans, provided in one of the first and second radio units, forgenerating a first reference code; establishing means for establishing aradio link between the first radio unit and the second radio unit;comparing means provided in the other one of the first and second radiounits for comparing said first reference code generated by said one ofthe first and second radio units with a second reference code previouslystored in said other one of the first and second radio units;transmitting means for transmitting the identification code stored inthe first radio unit to the second radio unit over the established radiolink; and storing means provided in the second radio unit for storingthe identification code transmitted from the first radio unit inresponse to a match of the compared first and second reference codes. 2.The radio telecommunication system according to claim 1, furthercomprising:sending means for sending the identification code stored inthe storing means back to the first radio unit; comparing means forcomparing the identification code sent back to the first radio unit withthe identification code stored in the first radio unit; and indicationmeans for indicating to a user of the first radio unit whether theidentification code sent back to the first radio unit matches theidentification code stored in the first radio unit in response to aresult of the comparison by the comparing means.
 3. The radiotelecommunication system according to claim 1, wherein the generatingmeans comprises input means for inputting the reference code and storingmeans for storing the reference code input by the input means.
 4. Amethod of registering an identification code stored in a first radiounit into a second radio unit, comprising the steps of:generating afirst reference code at one of the first and second radio units;establishing a radio link between the first radio unit and the secondradio unit; transmitting the first reference code from said one of thefirst and second radio units to the other one of the first and secondradio units over the established radio link; comparing said firstreference code with a second reference code previously stored in saidother one of the first and second radio units; transmitting theidentification code stored in the first radio unit to the second radiounit over the established radio link; and storing the identificationcode transmitted from the first radio unit into the second radio unit inresponse to a match of the compared first and second reference codes. 5.The method according to claim 4, further comprising the steps of:sendingthe identification code transmitted from the first radio unit and storedin the second radio unit back to the first radio unit; comparing theidentification code sent back to the first radio unit with theidentification code stored in the first radio unit; and informing a userof the first radio unit whether the identification code sent back to thefirst radio unit matches the identification code stored in the firstradio unit.
 6. The method according to claim 4, wherein the step ofgenerating a reference code includes the steps of inputting thereference code and storing the reference code in each of the first andsecond radio units.
 7. The method according to claim 4, wherein the stepof establishing a radio link comprises the steps of transmitting signalsover a predetermined radio channel at one radio unit and receivingsignals over a predetermined radio channel at the other radio unit.
 8. Aradio telephone system, comprising:a base unit connected to a telephoneline; a radio telephone set comprising means for coupling said radiotelephone set through a radio link to said base unit; means forelectrically connecting said base unit to said radio telephone set;first memory means disposed in said base unit to be optionally writtentherein; second nonvolatile memory means disposed in said radiotelephone set and having an identification code previously writtentherein which is not previously stored within said base unit; means forwriting in said first memory means said identification code previouslywritten in said second memory means, through said radio link; means forinputting an input secret number; means for comparing said input secretnumber with a preset secret number and for producing a coincidenceoutput when said input secret number and said preset secret numbercoincide; and means for enabling operation of said writing means onlywhen said comparing means produces a coincidence output.
 9. A radiotelephone system as set forth in claim 8, wherein said first memorymeans has power source backup means.
 10. A radio telephone system as setforth in claim 8, wherein said first memory means stores an abbreviateddial number together with said identification code.
 11. A radiotelephone system as set forth in claim 8, wherein a plurality of saidradio telephone sets are provided each having a corresponding one ofsaid identification codes written in said respective first memory meansand said base unit further comprises means for selectively calling therespective radio telephone sets on the basis of said plurality ofidentification codes.
 12. A radio telephone system as set forth in claim8, wherein said base unit further comprises third nonvolatile memorymeans for storing therein said identification code.
 13. A radiotelephone system as set forth in claim 8, further comprising:means fortransferring to said base unit said identification code written in saidsecond memory means; and means provided in said base unit for comparingsaid transferred identification code with said identification codepreviously written in said first memory means thereby confirming if saididentification code is correctly written in said second memory means.14. A radio telephone system as set forth in claim 8, wherein saidwriting means comprises:means for electrically connecting said base unitto said radio telephone set; means for producing a detecting output uponcompletion of an electrical connection between said base unit and saidradio telephone set; and manual input means operable in response to thepresence of said detecting output to start writing in said first memorymeans said identification code previously written in said second memorymeans.
 15. A radio telephone system as set forth in claim 14, whereinsaid manual input means is provided in said radio telephone set.
 16. Aradio telephone system as set forth in claim 14, wherein said manualinput means is provided in said base unit.